Rotary driven pipe-bursting tool

ABSTRACT

An apparatus for bursting pipe is preferably adapted to receive rotational energy from the inner member of a dual-member drill string. In a preferred embodiment, a plurality of pipe-bursting members, driven by the interconnected inner members, cut or burst a subterranean pipe. In another preferred embodiment, a plurality of screw drives move the pipe-bursting members between an expanded position and a retracted position in response to rotation of the interconnected inner members.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation in part of application Ser. No.10/287,270, filed Nov. 4, 2002, now U.S. Pat. No. 6,896,077, issued May24, 2005.

FIELD OF THE INVENTION

This invention relates generally to preparation for trenchlessreplacement of old pipe, and in particular to the bursting or cutting ofsubterranean pipe to allow the insertion of new pipe therein.

BACKGROUND OF THE INVENTION

Trenchless replacement of existing subterranean pipelines provides anefficient and cost effective way of replacing aged pipe and/or expandingthe capacity of existing pipe. Several devices have been developed toaccomplish these objectives. However, there remains an ongoing need forimproved pipe replacement tools.

SUMMARY OF THE INVENTION

The present invention is directed to a pipe-bursting apparatus for usewith a dual-member drill string. The drill string comprises an outermember and an inner member. The inner member is rotatable independentlyof the outer member. The apparatus comprises a frame connectable withthe drill string, a drive assembly, a rod and a pipe-bursting member.The drive assembly is supported by the frame and operable in response torotation of the inner member of the drill string. The rod is rotatablysupported within the frame and rotatable in response to operation of thedrive assembly. The pipe-bursting member is operatively connected to therod and operable in response to rotation of the rod.

The present invention further includes a pipe-bursting apparatus for usewith a dual-member drill string. The dual-member drill string comprisesan outer member and an inner member. The inner member is rotatableindependently of the outer member. The pipe-bursting apparatus comprisesa frame connectable with the dual-member drill string, a rod, aplurality of pipe-bursting members, and a plurality of screw drives. Therod is rotatably supported within the frame and connectable with theinner member of the drill string. The plurality of pipe-bursting membersare operatively connected to the frame. The plurality of screw drivesare supported by the frame and operable in response to rotation of therod. Operation of at least on of the screw drives operation of thepipe-bursting members.

The present invention also includes a horizontal directional drillingsystem. The system comprises a drive machine, a dual-member drillstring, and a pipe-bursting apparatus. The dual-member drill string hasa first end and a second end. The first end of the drill string isoperatively connected to the drive machine. The drill string comprisesan inner member and an outer member. The inner member is moveableindependently of the outer member. The pipe-bursting apparatus isoperatively connected to the second end of the drill string so thatmovement of the inner member drives operation of the apparatus. Thepipe-bursting apparatus comprises a frame, a rod, a plurality ofpipe-bursting members, and a plurality of screw drives. The rod isrotatably supported within the frame and operable in response tomovement of the inner member of the drill string. The plurality ofpipe-bursting members are operatively connected to the frame. Theplurality of screw drives are supported by the frame and operable inresponse to rotation of the rod. At least one of the plurality of screwdrives operation of the plurality of pipe-bursting members.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic representation of a near surface horizontaldirectional drilling machine acting on an uphole end of a drill stringthat, in turn, supports a pipe-bursting apparatus constructed inaccordance with the present invention connected to a new pipe.

FIG. 2 shows a fragmented, side elevational, partly sectional view of afirst type pipe section used with a dual-member drill string.

FIG. 3 is a fragmented, side elevational, partly sectional view of analternative type pipe section used with a dual-member drill string. Inthis type of pipe section, the pin end and box end of the inner memberare reversed.

FIG. 4 is a fragmented, side elevational, partly sectional view of apreferred drive machine used with the present invention.

FIG. 5 is a side elevational, partly sectional view of a firstembodiment of the pipe-bursting apparatus wherein the pipe-burstingmember is a pivoting linkage.

FIG. 6 is a perspective view of the pipe-bursting apparatus of FIG. 5.

FIG. 6 a is a side elevational, partly sectional view of an alternativeembodiment of the pipe-bursting apparatus of FIGS. 5 and 6. Thepipe-bursting apparatus of FIG. 6A has a pipe splitting member inaddition to the pivoting linkage of FIGS. 5 and 6.

FIG. 7 is a side elevational, partly sectional view of anotherembodiment of the pipe-bursting apparatus of the invention. Theapparatus of FIG. 7 takes the form of a pipe-bursting member having apivotally mounted pipe-bursting wedge. In this embodiment, a singlepipe-bursting wedge is operated by a moveable collar.

FIG. 7A is a side-elevational, partly sectional view of an alternativeembodiment of the pipe-bursting apparatus of FIG. 7. The apparatus ofFIG. 7A has a plurality of pivotally mounted pipe-bursting wedges thatare operated by opposing moveable collars.

FIG. 8 is a fragmented, side elevational, partly sectional view ofanother embodiment of the pipe-bursting apparatus. The apparatus of FIG.8 has a pipe-bursting member comprised of oscillating blades.

FIG. 9 is a sectional view of an alternative embodiment of thepipe-bursting apparatus. The apparatus of FIG. 9 has a pipe-burstingmember comprised of a splitting member driven by the operation ofhydraulic cylinders.

FIG. 10 shows a modification of the pipe-bursting apparatus of FIG. 9.The hydraulic pressure necessary to drive the hydraulic cylinders isgenerated above-ground and pumped downhole to the pipe-burstingapparatus along a single-member drill string.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Turning now to the drawings in general, and FIG. 1 in particular, thereis shown therein a horizontal directional drilling machine 10. FIG. 1illustrates the usefulness of horizontal directional drilling bydemonstrating that a replacement pipe 12 can be installed without theneed for trenching along the desired path. To install the replacementpipe 12, a drill string 14 is inserted through the old pipe 16 andemerges from an exit pit 18. The downhole end 20 of the drill string 14is then coupled to the replacement pipe 12, and the replacement pipe istowed through the existing borehole 22 as the old pipe 16 is burst.Considerable force is necessary to burst the old pipe 16 and pull thenew pipe 12 through the burst pipe 26. As used herein, “burst” or“pipe-bursting” means bursting, cutting, fragmenting or any other actionwhich ruptures the old pipe 16 to permit replacement thereof. Thepresent invention is directed to devices and methods for improvingpipe-bursting and old pipe replacement operations.

The horizontal directional drilling machine 10 generally comprises aframe 28 for supporting a drive machine 30. The drive machine 30 ismovably supported on the frame 28 between a first position and a secondposition. Movement of the drive machine 30, by way of an axial movementmeans (not shown), between a first position and a second positionaxially retracts or advances the drill string 14 and pipe-burstingapparatus 24 through the borehole 22.

The drill string 14 is operatively connected to the drive machine 30 atan uphole end 32. A pipe-bursting apparatus 24 is coupled to thedownhole end 20 of the drill string 14. In the present invention thedrill string 14 transmits torque and thrust to the pipe-burstingapparatus 24 to break up the old pipe 16.

In accordance with several aspects of the present invention, it ispreferable to utilize a dual-member drill string. The dual-member drillstring 14 may comprise a plurality of dual-member pipe sections. Anydual-member drill string capable of transmitting torque from the drivemachine 30 to the pipe-bursting apparatus may be used. For purposes ofillustration, two different dual-member pipe sections, also called pipejoints, comprising the dual-member drill string will be discussed.

Turning now to FIG. 2, there is shown one of a plurality of dual-memberpipe sections 40 comprising the dual-member drill string 14. Thedual-member pipe section 40 comprises a hollow outer member 42 and aninner member 44 positioned longitudinally therein. The inner member 44and outer member 42 are connectable with the inner members and outermembers of adjacent dual-member pipe sections to form the dual-memberdrill string 14 (FIG. 1). The interconnected inner members areindependently rotatable of the interconnected outer members to driveoperation of the pipe-bursting tool 24.

The outer member 42 is preferably tubular having a pin end 46 and a boxend 48. The pin end 46 and the box end 48 are correspondingly threaded.The pin end 46 is provided with tapered external threads 50, and the boxend 48 is provided with tapered internal threads 52. Thus, the box end48 of the outer member is connectable to the pin end 46 of a likedual-member pipe section 40. Similarly, the pin end 46 of the outermember 42 is connectable to the box end 48 of a like dual-member pipesection 40.

The external diameter of the pin end 46 and the box end 48 of the outermember 42 may be larger than the external diameter of the central bodyportion 54 of the outer member 42. The box end of the outer member 42forms an enlarged internal space 56 for a purpose yet to be described.

The inner member 44 is preferably elongate. In a preferred dual-memberpipe section 40, the inner member 44 is integrally formed and comprisesa solid rod. However, in some instances a tubular inner member 44 may besatisfactory.

Preferably, the inner member 44 of the dual-member pipe section isprovided with a geometrically-shaped pin end 58 and with a box end 60forming a geometrically-shaped recess corresponding to the shape of thepin end 58 of the inner member 44. As used herein,“geometrically-shaped” denotes any configuration that permits the pinend 58 to be slidably received in the box end 60 and yet transmit torquebetween adjacent pipe sections 40. The geometrically-shaped pin end 58and box end 60 prevent rotation of the pin end 58 relative to the boxend 60 when thus connected. A preferred geometric shape for the pin end58 and box end 60 of the inner member 44 is a hexagon. The box end 60 ofthe inner member 44 may be pinned, forged, welded or attached to theinner member by any suitable means.

The box end 60 of the inner member 44 is disposed within the box end 48of the outer member 42. It will now be appreciated that the box end 48of the outer member 42 forms an enlarged internal space 56 for housingthe box end 60 of the inner member. This arrangement facilitates easyconnection of the dual-member pipe section 40 with adjacent pipesections, the drill string 14, and the drive machine 30.

It is desirable to construct the dual-member pipe section 40 so that theinner member 44 is slidably insertable in and removable from the outermember 42. This allows easy repair and, if necessary, replacement of theinner member 44. However, longitudinal movement of the inner member 44within the outer member 42 should be restricted in the assembleddual-member pipe section 40. Accordingly, stop devices usually areprovided in the dual-member pipe section 40.

The pipe section 40 may have an annular shoulder 62 formed on the innersurface 64 of the outer member 42 to limit longitudinal movement of theinner member 44 within the outer member. In addition, the box end 60 ofthe inner member 44 forms a shoulder 66 which is larger than the annularshoulder 62. Thus, when the inner member 44 is moved in direction X, theshoulder 66 abuts annular shoulder 62 preventing further movement inthat direction.

Longitudinal movement of the inner member in the direction of the boxends 48 and 60, designated as direction Y in FIG. 2, preferably also isrestricted. The pin end 58 of the inner member 44 extends a distancebeyond the pin end 46 of the outer member 42. A radially projectingannular stop member 68 is disposed near the pin end 58 of the innermember 44 beyond the pin end 46 of the outer member 42. As shown inexploded view in FIG. 2, the radially projecting annular stop member 68preferably comprises a collar and a set screw or pin 70. When the innermember 44 is moved in direction Y, the stop member collar 68 abuts thepin end 46 of the outer member 42 and obstructs further movement.

Turning now to FIG. 3, there is shown an alternative dual-member pipesection 40A. The pipe section 40A comprises a hollow outer member 42Aand an inner member 44A positioned longitudinally therein. The innermember 44A is preferably elongate and has a pin end 58A and a box end60A. As previously discussed, the pin end 58A and box end 60A may begeometrically-shaped to transmit torque between adjacent pipe sections.

The geometrically-shaped pin end 58A of pipe section 40A is disposedwithin the box end 48A of the outer member 42A. The box end 48A of theouter member 42A forms an enlarged internal space 56A for receiving thebox end 60A of a similarly formed dual-member pipe section.

The inner member 44A is positioned within the outer member 42A so as toextend to an external point beyond the pin end 46A of the outer member.The inner member box end 60A is formed by a geometrically-shaped drivecollar 71 connected to the external portion of the inner member 44A. Thedrive collar 71 is preferably attached to the inner member using a rollpin (not shown), but may be attached to the inner member 44A by anyother suitable means. The drive collar 71 has an internalgeometrically-shaped bore 72 which corresponds with thegeometrically-shaped pin end 58A of the inner member 44A. Use of thegeometrically-shaped drive collar 71 provides a connection capable oftransmitting torque between adjacent pipe sections 40A and ultimately tothe pipe-bursting apparatus 24.

Turning now to FIG. 4, the drive machine 30 for driving operation of thepipe-bursting apparatus 24 is shown in more detail. Because the outermember 42 and inner member 44 rotate independently of each other, thedrive machine 30 has two independent drive groups for driving the outermembers independently of the inner members.

The drive machine 30 thus preferably comprises a carriage 74 supportedon the frame 28. Supported by the carriage 74 is an outer member drivegroup 76 and an inner member drive group 78. The outer member drivegroup 76 drives the outer member 42. The inner member drive group 78drives the inner member 44 and the pipe-bursting apparatus 24. The drivemachine 30 also comprises a biasing assembly 80 for urging engagement ofthe pipe sections. A suitable drive machine 30 having an outer memberdrive group 76 for driving the outer member 42, and an inner memberdrive group 78 for driving the inner member 44 is disclosed in moredetail in U.S. Pat. No. 5,682,956, the contents of which areincorporated herein by reference.

Turning now to FIGS. 5 and 6, there is illustrated therein a firstembodiment of the pipe-bursting apparatus 24A for use with thepreviously described horizontal directional drilling system. Thepipe-bursting apparatus 24A includes a frame 102 having an uphole end104 and a downhole end 106. The uphole end 104 has external threads 108for connecting to the outer member 42A of the dual-member drill string14. As seen in FIG. 6, the frame 102 of the present embodiment maygenerally be characterized as a housing within which is supported a rod110. Additionally, the frame 102 is preferably constructed to haveopenings 120 formed on the body of the frame.

As illustrated in FIG. 5, the downhole end 106 of the frame 102 may haveinternal threads 112 for connecting to an expansion bell 114. Theexpansion bell 114 is constructed to force fragments of the old pipe 16(FIG. 1) into the surrounding soil and allows for the replacement pipeto be drawn into the borehole. The expansion bell 114 may be constructedto include a connection member 116 to allow towing of the replacementpipe 12 (FIG. 1) into the borehole.

External threads 108, on the uphole end 104 of the housing 102, providea connection that is capable of transmitting torque from the outermember 42A of the drill string 14 to the pipe-bursting apparatus 24A forpositioning and rotationally orienting the apparatus within the borehole12.

The rod 110 is rotatably supported on the frame 102 and connectable withthe inner member 44A of the drill string 14. In the present embodiment,the rod 110 threadedly engages a movable collar 122 supported within theframe 102. The rod 110 and movable collar 122 function as a screw drivefor operation in response to rotation of the inner member 44A. Movementof the collar 122 in response to rotation of the rod causes thepipe-bursting member 118 to move between an expanded and retractedposition.

As shown in FIGS. 5 and 6, the pipe-bursting member 118 may comprise apipe-engaging wedge 124 driven by the moveable collar 122. Thepipe-engaging wedge 124 is preferably elongate having a generally flatunderside 126, a lengthwise groove 128, and a tapered edge 130. Thegroove 128 formed on the underside 126 of the wedge 124 extends theentire length of the wedge and is used for a purpose yet to bedescribed. The tapered edge 130 engages the old pipe 16 (FIG. 1) andcauses bursting of the old pipe. The tapered edge 130 may be formed fromany resilient material able to withstand repetitive localized pressureagainst the old pipe 16 (FIG. 1).

The pipe-engaging wedge 124 is operatively connected to the movablecollar 122 and the frame 102 by arms 132 and 134. Arm 132 is preferablyconnected to the movable collar 122 at one end and the pipe-engagingwedge 124 at the other end. The wedge 124 is moveably connected to theframe 102 by arm 134. The movable arms 132 and 134 link rotation of therod 110 to movement of the pipe-engaging wedge 124.

With reference to FIG. 5, self-locking pins 136 may be used to pivotallyconnect the arms 132 and 134 to each of the pipe-engaging wedge 124,movable collar 122 and frame 102. Pins 136 permit replacement of thewedge 124, when worn, or the substitution of wedges having differentconfigurations, when necessary. Use of pins 136 to mount the wedge 124to the arms 132 and 134 permits pivotal movement of the wedge betweenthe retracted and expanded position. It will be appreciated thatattaching the wedge 124 to arms 132 and 134 is not limited to the use ofself-locking pins 136. Alternatively, threaded bolts or screws could beused in place of the pins 136.

The movable collar 122 may be generally cylindrical having an internallythreaded bore 138 engaging the correspondingly threaded segment 140 ofthe rod 110. Threaded engagement between the rod 110 and the collar 122causes the collar to travel in response to rotation of the rod. Theextension of arms 132 and 134 through opening 120 prohibits rotation ofthe movable collar within the frame 102. The movable collar 122 may havean external groove 142 for receiving arm 132 when the pipe-burstingmember 118 is in the retracted position.

Continuing with FIG. 5, the rod 110 is rotatably mounted within thehousing 102. Bearings 144 and 145 support the rod 110 within the housing102 for co-axial rotation therein. Preferably, a geometrically-shapeddrive collar 146 is connected to the portion of the rod 110 extendingbeyond the uphole end 104 of the housing 102. The drive collar 146provides for easy connection with a correspondingly-shaped inner member.The use of a geometrically-shaped drive collar 146 to connect the innermember 44A (FIG. 3) of the dual-member drill string to the pipe-burstingapparatus 24A is preferred; however, connection may be accomplished inany way that allows for torque transmission from the inner member of thedrill string to the rod 110.

When the inner member 44A of the dual-member drill string 14 is rotatedin a first direction, the threaded segment 140 of the rod 110, formingpart of the screw drive, communicates with the corresponding internallythreaded bore 138 of the movable collar 122. This threaded interactioncauses the movable collar 122 to travel in direction X as the rod 110rotates. Moving the collar 122 in direction X causes arms 132 and 134and wedge 124 to move to the expanded position. This causes the taperededge 130 of the wedge 124 to engage and rupture the old pipe 16 (FIG. 1)from within.

The pipe-bursting wedge 124 is moved to the retracted position byrotating the inner member of the drill string 14 the opposite or seconddirection. This reverses the effect of the screw drive by moving thecollar 122 in direction Y. Moving the collar 122 in direction Y movesthe bursting wedge 124 to a retracted position. As the collar 122 ismoved in direction Y, the arm 132 retracts into both the wedge groove128 and collar groove 142.

Now, it will be understood that the pipe-bursting apparatus of FIGS. 5and 6 is preferably used in a step-wise fashion along the length of theold pipe. The pipe-bursting apparatus is axially advanced in theretracted position to the desired point within the old pipe. Iforientation of the bursting device within the bore is deemed to becritical, the outer member of the drill string may be rotated toproperly orient the pipe-bursting apparatus. Once the pipe-burstingapparatus is properly positioned within the old pipe, the inner memberis rotated to expand the pipe-bursting member and burst the old pipe.After the pipe-bursting member has been radially expanded to burst theold pipe, the inner member is rotated in the opposite, or seconddirection to move the pipe-bursting apparatus into the retractedposition. The apparatus is axially advanced to the next segment ofunbroken old pipe and the process is repeated. The process is continueduntil the desired length of old pipe has been burst and the replacementpipe inserted in its stead.

As shown in FIG. 6, it will be appreciated that the housing 102 ofpipe-bursting apparatus 24A may be constructed to have multiple openings120 so that multiple pipe-bursting members 118 may be used.

Referring now to FIG. 6A, there is shown therein an alternativeembodiment of the pipe bursting apparatus FIG. 24A shown in FIGS. 5 and6. The pipe-bursting apparatus 25 of FIG. 6A includes a frame 148 havingan uphole end 150 and a downhole end 152, a drive assembly 154 supportedby the frame, a rod 156, pipe-bursting member 118A operatively connectedto the rod, and an expansion bell 160. The pipe-bursting apparatus 25 isconnectable with the outer member 42A of the dual-member drill stringusing external threads 108.

The drive assembly 154 is supported by the frame 148 and may comprise aplanetary gear system 162 and a drive shaft 164. The drive shaft 164 isconnected to the inner member 44A of the drill string 14 using drivecollar 146. Drive collar 146 allows for the transmission of rotationalenergy from the inner member 44A to the drive shaft 164. The planetarygear system 162 translates the rotational energy from the drive shaft164 to a low speed, high torque rotational force exerted on the rod 156.

The rod 156 threadedly engages a movable collar 166 supported within theframe 148. The rod 156 and movable collar 166 function as a screw drivesimilar the screw drive discussed with reference to FIGS. 5 and 6.Movement of the collar 166 in response to rotation of the rod 156 causesthe pipe-bursting member 118A to move between the expanded position,illustrated in FIG. 6A, and a retracted position.

As previously discussed, the pipe-bursting member 118A may comprise apipe-engaging wedge 124A driven by the movable collar 166. Thepipe-engaging wedge 124A is operatively connected to the movable collar166 and the frame 148 by arms 132 and 134. The movable arms 132 and 134link rotation of the rod 156 to movement of the pipe-engaging wedge124A.

The movable collar 166 may be generally cylindrical having an internallythreaded bore 168 engaging the correspondingly threaded segment 140 ofthe rod 156. Threaded engagement between the rod 156 and the collar 166causes to collar to travel along the rod and extends the arms 132 and134 through opening 120. Positioning of the wedge 124A and the arms 132and 134 within the opening 120 limits rotation of the movable collar 166within the frame 148.

Referring still to FIG. 6A, the pipe-bursting apparatus 25 may comprisea movable expansion bell 160. The expansion bell 160 is adapted tothreadingly engage the threaded segment 172 of the rod 156 so that theexpansion bell travels axially in response to rotation of the rod.

The expansion bell 160 may comprise a pipe-engaging portion 174 and abody 176. The pipe-engaging portion 174 of the expansion bell 160 ispreferably conical, increasing in diameter from uphole to downhole. Thediameter of the pipe-engaging portion 174 may be just slightly largerthan the outer diameter of the replacement pipe 12. The conical shapeand large diameter of the pipe-engaging portion 174 of the expansionbell 160 functions to burst the old pipe and force it into thesurrounding soil. The pipe-engaging portion 174 of the expansion bell160 may support pipe-cutting blades 178. Pipe-cutting blades 178 areadapted to cut the old pipe as the expansion bell 160 is moved axiallyin direction X and may be constructed of a material resilient enough towithstand the forces exerted upon the blades. The expansion bell 160 mayalso include the connection member 116 to allow towing of thereplacement pipe 12 into the borehole.

The body 176 of the expansion bell 160 may be generally cylindricalhaving an internal bore 180 engaging the second threaded portion 172 ofthe rod 156. Threaded engagement between the rod 156 and the body 176allows the expansion bell 160 to move axially relative to the frame 148in response to rotation of the rod. It will be appreciated that theexpansion bell 160 is non-rotatably supported within the frame 148 sothat it does not rotate with the rod 156. Therefore, the body 176 mayhave a plurality of elongated recesses 182, disposed circumferentiallyabout the body and correspondingly aligned with elongated recesses 184spaced about the inner surface 186 of the frame 148. Ball bearings 188may be placed between each recess 182 and its corresponding recess 184to prevent rotation of the expansion bell 160 relative to the frame 148.The elongated recesses 182 and 184 in conjunction with ball bearings 188also function to limit axial movement of the expansion bell 160 to thetravel distance of the ball bearings.

When the inner member 44A of the dual-member drill string 14 is rotatedin a first direction, the threaded segment 140 of the rod 156, formingpart of the first screw drive, communicates with the correspondinginternally threaded bore 168 of the movable collar 166. The threadedinteraction between the collar 166 and the threaded segment causesmovement of the pipe-engaging wedges 124A as previously discussed withreference to FIGS. 5 and 6. However, rotation of the rod 156 alsorotates the threaded segment 172, forming part of the second screwdrive. The interaction between the threaded segment 172 and internalbore 180 causes the expansion bell 160 to move in direction X and engagethe old pipe.

The rod 156 is then rotated in the second direction to retract thepipe-bursting wedge 124A. Additionally, the second threaded segment 172is rotated in the second direction and the expansion bell 160 isextended from the frame 148 as the rod is rotated and the frame furtherwithdrawn into the old pipe. The bursting operation is then repeated ina substantially step-wise fashion until the desired length of old pipehas been burst.

Turning now to FIG. 7, there is shown an alternative embodiment of apipe-bursting apparatus 24B. The pipe-bursting apparatus 24B isconnectable to a dual-member drill string and comprises a frame 204, arod 206 rotatably supported on the frame, and a pipe-bursting member 208drivingly connected to the rod. The pipe-bursting member 208 is operablein response to rotation of the rod 206. The embodiment of FIG. 7illustrates a pipe-bursting member 208 comprising at least onepipe-engaging wedge 210 pivotally connected to the frame 204 andmoveable between an expanded position and a retracted position inresponse to rotation of the rod.

The frame 204 comprises an uphole end 212 having external threads 214for connecting the apparatus 24B to the box end of a correspondinglythreaded outer member of a dual-member drill string (FIG. 3).

The rod 206, having a first end 216 and a second end 218, is supportedby bearings 220 and 222 for co-axial rotation within the frame 204. Thefirst end 216 of the rod 206 may comprise a geometrically-shaped box end224 for connection with the correspondingly shaped pin end of the innermember 44A of a dual-member drill string 40A (FIG. 3).

The second end 218 of the rod 206 comprises a screw drive system 226 todrive operation of the pipe-bursting member 208. The screw drive system226 comprises a screw 228 and a movable collar 230. The movable collar230 has an internal bore 232 to threadedly receive the screw 228. Themovable collar 230 is non-rotatably supported by the frame 204 andmovable between a first position and a second position in response torotation of the screw 228. Axial movement of the collar 230 to theposition shown in FIG. 7 causes the collar to laterally expand thepipe-engaging wedge 210.

The pipe-engaging wedge 210 is pivotally connected to the frame 204 byself-locking pin 236. Use of pin 236 permits replacement of the wedge210 when worn and allows pivotal movement of the wedge in response torotation of the rod 206.

After the apparatus 24B has been properly oriented by rotating the outermembers of the dual-member drill string, the inner member of the drillstring is rotated to radially extend the pipe-engaging wedge 210.Extension of the pipe-engaging wedge 210 will cause the wedge to contactthe inner wall of the old pipe. As the wedge 210 is forced outward, itwill cause the wall of the old pipe to fracture at the point of contact.After local fracture of the old pipe, the rod 206 is counter-rotated tocause the wedge 210 to retract. The pipe-bursting apparatus 24B is thendrawn forward within the old pipe to the next position. As thepipe-bursting apparatus is drawn forward, an expansion bell 238 willcause the fractured pipe to further fracture and force the old pipefragments into the surrounding soil. After advancement of the pipebursting apparatus 24B, the expansion process is repeated to causeanother local fracture of the old pipe. This cycle is repeated along thelength of the pipe to be replaced.

Referring now to FIG. 7A, there is shown therein an alternativeembodiment of the pipe-bursting apparatus 24B of FIG. 7. Pipe-burstingapparatus 27 is connectable to a dual-member drill string and comprisesa frame 240, a rod 242 rotatably supported on the frame, a firstpipe-bursting member 244 and a second pipe-bursting member 246 bothdrivingly connected to the rod. The first pipe-bursting member 244 andsecond pipe-bursting member 246 are operable in response to rotation ofthe rod 242. The embodiment of FIG. 7A illustrates the use of multiplepipe-bursting members 244, 246 each comprising pipe-engaging members 248and 249 pivotally connected to the frame 240 using pins 236 and moveablebetween an expanded position and a retracted position in response torotation of the rod 242.

The frame 240 comprises an uphole end 250 having external threads 252for connecting the apparatus 27 to the box end of a correspondinglythreaded outer member 42A of a dual-member drill string 14 (FIG. 3).

The rod 242 has a first end 254 and a second end 256 and is supportedfor co-axial rotation within the frame 240 by bearings 258. The firstend 254 of the rod 242 may be operatively connected to the driveassembly 154. The drive assembly 154 may be supported by the frame 240and may comprise a planetary gear system 162 and a drive shaft 164. Thedrive shaft 164 is connectable to the inner member 44A of the drillstring 14 (FIG. 3) using drive collar 146. The planetary gear system 162translates rotational energy from the drive shaft 164 to a low speed,high torque rotational force exerted on the rod 242.

The rod 242 comprises a first screw drive system 260 and a second screwdrive system 262 to drive operation of the first pipe-bursting member244 and the second pipe-bursting members 246. The first screw drivesystem 260 may comprise a left-hand screw 264 and a first movable wedge266. The second screw drive system 264 may comprise a right-hand screw268 and a second movable wedge 270. The movable wedges 266 and 270 bothhave internal bores 272 and 274 to threadedly receive the screws 264 and268. The movable wedges 266 and 270 are non-rotatably supported by theframe 240 in slots 276 and 278, but movable axially between a firstposition and a second position in response to rotation of the screws 264and 268. The movable wedges 266 and 270 are generally conical so thataxial movement of the first wedge 266 in direction Y and the secondwedge 270 in direction X causes the pipe-engaging members 248 and 249 tolaterally expand from the frame 240.

In operation, the apparatus 27 is positioned and oriented by rotatingthe outer members 42A of the dual-member drill string 14. The innermember 44A of the drill string 14 is rotated in a first direction torotate the rod 242 and to laterally extend the pipe-engaging members 248and 249 from the frame 240. Extension of the pipe-engaging members 248and 249 exerts opposing forces on the old pipe and causes eventualfracturing of the old pipe. After the old pipe has been fractured, theinner member 44A is rotated in a second direction to move the wedge 266in direction X and wedge 270 in direction Y. Moving the wedges 266 and270 in such a manner allows the pipe-bursting members 248 and 249 toretract into the frame 240. After the pipe-engaging members 248 and 249have been retracted, the pipe-bursting apparatus 27 is moved to the nextsegment of pipe for bursting.

Turning now to FIG. 8, there is shown another embodiment of thepipe-bursting apparatus. In this embodiment, the pipe-bursting apparatus24C has a pipe-bursting member 300 comprised of oscillating blades 302.The embodiment of FIG. 8 illustrates the use of a pair of bladesconnected to opposing sides of the housing, however, it will beappreciated that the number of blades may be altered without departingfrom the spirit of the present invention.

The pipe-bursting apparatus 24C may be constructed so that it isconnectable to any dual-member drill string 14 (FIG. 1). However, forpurposes of illustration, pipe-bursting apparatus 24C is shown connectedto pipe section 40, previously discussed with reference to FIG. 2. Thepipe-bursting apparatus 24C comprises a frame 304 and a rod 306rotatably supported within the frame. The frame 304 comprises an upholeend 308 and a downhole end 310. The uphole end 308 comprises externalthreads 312 for connecting to the box end 48 of a correspondinglythreaded pipe section 40. The downhole end 310 of the frame 304 isadapted for connection to a swivel connector assembly 314. A pipe puller(not shown) may be attached to the connector assembly 314 for towing thenew pipe into the borehole as the pipe-bursting apparatus 24C is axiallyadvanced.

Referring still to FIG. 8, the first end 316 of rod 306 may comprise ageometrically-shaped pin end 318. The pin end 318 allows for connectionwith the correspondingly shaped box end 60 of the inner member 44 of thedual-member pipe section 40. Bearings 320 and 321 support the second end322 of the rod 306 for rotation within the frame 304.

The pipe-bursting member uses pivotally mounted blades 302 to burst theold pipe. The blades 302 are mounted to the frame 304 using self-lockingpins 334. The use of self-locking pins 334 allows for easy replacementor substitution of the blades. The blades 302 are generally elongate andhave a pipe-engaging surface 336. A generally rounded projection 340 isformed on the underside 338 of the blade 302. The rounded projection 340is adapted to be engaged by rotating cam members, described hereinafter.The blade 302 may be constructed from a resilient material such as casehardened steel which is capable of withstanding repeated impact of thepipe-engaging surface 336 with the old pipe.

The pipe-bursting member 300 further comprises a cam system 326supported on the rod 306. The cam system 326 comprises a plurality ofcylindrical cam members 328 having an eccentrically positionedthrough-hole 332. The cylindrical cam member is supported on the rod 306for fixed rotation therewith using a key member 333. However, thethrough-hole 332 may be geometrically-shaped to transfer torque from therod 306 to cam member 328. The cam members 328 may further comprise ballor roller bearing 330 adapted to roll past the rounded projection 340 asthe cam member 328 is rotated with the rod 306.

The cam members 328 may be oriented to cause oscillation of the blades302 in any one of several patterns. The inner member drive group 78 ofthe drive machine 30 (FIG. 4) rotates the rod 306. Rotating the rod 306causes rotation of the cam members 328 within the frame 304. Inoperation, either the cam members 328 or the bearings 330 may contacttheir corresponding blades during only a portion of one revolutionbecause of the eccentric position of the through-holes 332.

The shape of the frame 304 is preferably conical, increasing in diameterfrom the uphole end 308 to the downhole end 310. The preferred conicalshape of the frame 304 allows for the uphole end 308 to pass through theexisting inner diameter of the pipe being replaced with littleresistance. The diameter of the downhole end 310 may be just slightlylarger than the outer diameter of the replacement pipe. This shapeallows the frame 304 to force the fractured pipe into the surroundingsoil.

As the pipe-bursting apparatus 24C is pulled back by the horizontaldirectional drilling machine 10 (FIG. 1), the replacement pipe is pulledinto the newly expanded borehole. The outer member of the drill stringmay be rotated by the drive machine 30 (FIG. 1) to orient thepipe-bursting apparatus 24C. The inner member transmits torque to therod 306 by way of the geometrically-shaped connection between the rod306 and the box end 60 of the inner member. The cam members 328 arerotated with the rod 306. In the embodiment of FIG. 8, rotation of theeccentrically-shaped cam members 328 causes the bearings 330 to engagethe rounded projections 340. This engagement forces the blades to pivotand expand radially from the housing and thus burst the old pipe as thenew pipe is pulled into position.

Turning now to FIG. 9, there is shown therein another embodiment of apipe-bursting apparatus 24D constructed for the splitting andreplacement of underground pipes. Pipe-bursting apparatus 24D is adaptedto burst old pipes composed of ductile materials such as steel or iron.The pipe-bursting apparatus 24D of FIG. 9 utilizes a hydraulic pump 402to generate hydraulic pressure sufficient to pull the pipe-burstingmember 404 through the pipe to be replaced. The pipe-bursting apparatus24D comprises a frame 406, a rod 408 rotatably supported on the frame406, and the pipe-bursting member 404. Pipe-bursting apparatus 24D usesa gripper assembly 410 to provide the reaction force necessary towithstand the pull generated by the hydraulic cylinder assembly 412 indriving operation of a pipe-splitting bell 416.

As illustrated in FIG. 9, the frame 406 may generally be characterizedas a housing within which is supported the hydraulic pump 402 and therod 408. The frame 406 has external threads 418 for connecting to theouter member 42A (FIG. 3) of the dual-member drill string 14. Theexternal threads 418 provide a connection that is capable oftransmitting torque from the outer member 42A of the drill string 14 tothe pipe-bursting apparatus 24D for positioning and rotationallyorienting the apparatus within the old pipe.

The rod 408 is rotatably supported on the frame 406 by bearings 407 andconnectable with the inner member 44A (FIG. 3) of the drill string 14.In the present embodiment, the rod 408 operatively engages the hydraulicpump 402 supported within the frame 406. Preferably, ageometrically-shaped drive collar 420 is connected to the portion of therod 408 extending beyond the external threads 418 of the housing 406. Aspreviously discussed, the drive collar 420 provides for easy connectionwith a correspondingly-shaped inner member 42A (FIG. 3).

The pipe-bursting apparatus 24D is adapted so that the hydraulic pump402 may supply pressurized fluid to the gripper assembly 410 andhydraulic cylinder assembly 412 substantially simultaneously. Rotationof the rod 408 drives operation of the hydraulic pump 402 to pressurizethe hydraulic fluid. The hydraulic pump 402 draws hydraulic fluid from areservoir 422 having a collapsible bladder 424, via hose 426. Thepressurized fluid is then supplied to the gripper assembly 410 and tothe cylinder assembly 412 through hose 430.

A control valve 428 controls the flow of hydraulic fluid to and from thereservoir 422 through the suction hose 426 and a return hose 427. Thefluid is pulled from the reservoir 422, then passes through a hose 430to the gripper assembly 410. The hose 430 is connected to the gripperassembly housing 432 using a threaded connection 434. The fluid ispumped into a chamber 436 within the gripper assembly housing 432.

The fluid pumped into the gripper assembly housing 432 applies pressureto the pistons 438 and 440 to extend the pistons from the housing. Thepistons 438 and 440 each have a gripping means comprised of a pluralityof carbide buttons 442 which engage the inner wall of the pipe beingreplaced. The carbide buttons 442 provide frictional force necessary tohold the pipe-bursting apparatus 24D in place while the hydrauliccylinder assembly 412 is actuated. It will be appreciated that othermethods, such as machining or knurling the top surfaces of pistons 438and 440, may be used to facilitate the necessary gripping action.

While a gripping assembly composed of pistons 438 and 440 is disclosedherein, it is anticipated that other types of gripping devices may beused with the invention to accomplish the same purpose. For example,mechanical wedges could be extended from the gripper assembly 410 eitherthrough the action of hydraulic cylinders or screw-type actuators (notshown).

Hydraulic pressure within the gripper assembly 410 builds in response tothe resistance encountered by the pipe-splitting bell 416 as theapparatus 24D is pulled through the old pipe 16 (FIG. 1). In response toincreased hydraulic pressure, the pistons 438 and 440 are radiallyextended from the gripper assembly housing 432 to engage the innersurface of the old pipe 16 (FIG. 1) with increasing force. A shoulderbolt 444 and compression spring 446 regulate movement of the pistons 438and 440 within the housing 432. The compression spring 446 pulls thepistons 438 and 440 into the housing when the hydraulic pressure isdecreased.

The fluid chamber 436 is connected to the cylinder assembly 412 so thatthe hydraulic fluid may flow into the cylinder assembly 412 and thegripper assembly 410 substantially simultaneously. The hydrauliccylinder assembly 412 comprising hydraulic cylinders 448 and 450, pullsthe pipe-splitting bell 416 through the old pipe as the gripper assembly410 holds the pipe-bursting apparatus in a fixed position within the oldpipe. To pull the pipe-splitting bell 416 in direction X, both hydrauliccylinders 448 and 450 act upon a common cylinder rod 452.

The hydraulic cylinders 448 and 450 comprise downhole cavities 454 and456, and uphole cavities 458 and 460. Fluid is supplied to the downholecavities by conduits 462 and 464. The conduits 462 and 464 are formed inthe cylinder rod 452 and communicate with an internal bore 468 formed inthe cylinder rod. The uphole cavities 458 and 460 do not fill withhydraulic fluid, but have vents (not shown) to vent air from within thecavities to the outside environment.

The cylinder rod 452 is connected to the pipe-splitting bell 416 using athreaded connection (not shown). It will, however, be appreciated thatthe pipe-splitting bell 416 may be connected to the cylinder rod 452 inany manner sufficient to withstand the pulling force exerted on thepipe-splitting bell. The pipe-splitting bell 416 comprises one or morepipe-cutting blades 470 and is generally conical in shape. The conicalshape of pipe-splitting bell 416 forces fragments of the old pipe intothe surrounding soil and expands the existing borehole so that thereplacement pipe may be drawn into the borehole with little resistance.The blades 470 may be constructed of any material resilient enough towithstand the forces exerted upon them.

Referring to FIGS. 1 and 9, the apparatus 24D is connected to thedual-member drill string at the exit pit 18 using threads 418 and thegeometrically-shaped connector 420. After connection to the drillstring, the pipe-bursting apparatus 24D is drawn into the old pipe 16until the pipe-splitting bell 416 engages the old pipe 16. When tensionon the pipe-splitting bell 416 begins to increase, the inner member 44A(FIG. 3) of the drill string is rotated to activate the hydraulic pump402. In response to rotation of the inner member 44A, the control valve428 opens and the pump 402 draws hydraulic fluid from the reservoir 422and to the gripper assembly 410 and hydraulic cylinder assembly 412.

In response to the increased hydraulic pressure within the gripperassembly 410, the pistons 438 and 440 extend radially from the gripperassembly housing 432 to hold the pipe-bursting apparatus 24D in placeduring operation of the hydraulic cylinder assembly 412. As the pressurewithin the gripper assembly 410 increases, the hydraulic pressure withinthe hydraulic cylinder assembly 412 also increases to pull thepipe-splitting bell 416 through the old pipe 16 and cause the old pipeto split.

When the hydraulic cylinder assembly 412 has reached the end of itsstroke, rotation of the inner member 44A (FIG. 3) may be stopped therebyreducing the hydraulic pressure supplied to the gripper assembly 410 andthe hydraulic cylinder assembly 412. Reduction in the pressure suppliedto the gripper assembly 410 causes the compression springs 446 toretract the pistons 438 and 440. The horizontal directional drillingmachine 10 then pulls the apparatus 24D further into the old pipe untilthe hydraulic cylinder assembly 412 is extended back to its originalposition and the pipe-splitting bell 416 encounters resistancesufficient to warrant reactivating the hydraulic pump 402. When thehydraulic cylinders 448 and 450 are retracted, the oil in cavities 454and 456 flows back through hose 430, into control valve 428 where it isshunted back to the reservoir 422 through return hose 427. This cycle isrepeated until the desired length of old pipe has been burst.

The pipe-bursting apparatus 24D of FIG. 9 has been described hereinusing two hydraulic cylinders 448 and 450. It will, however, beappreciated that the apparatus may be modified to use one hydrauliccylinder instead of the two cylinders described herein. It will likewisebe appreciated that pipe-bursting apparatus 24D may employ three or morecylinders to perform the same function as the two hydraulic cylinders448 and 450.

Turning now to FIG. 10, there is illustrated therein an alternativeembodiment of the pipe-bursting apparatus 24D. The pipe-burstingapparatus 24E of FIG. 10 uses hydraulic pressure to burst the pipe to bereplaced 500. Hydraulic fluid is pressurized at a point uphole from thepipe-bursting apparatus 24E and pumped to the pipe-bursting apparatususing a hydraulic pump (not shown) and a hydraulic line 502. Thepipe-bursting apparatus of FIG. 10 has a gripper assembly 504, ahydraulic cylinder assembly 506, and a pipe-bursting member 508. Thepipe-bursting member is driven by cooperative operation of the gripperassembly 504 and the hydraulic cylinder assembly 506.

In the present embodiment, fluid is pumped through the borehole 22(FIG. 1) via the hydraulic hose 502 to a connector segment 510. Theconnector segment 510 is generally elongate and has external threads(not shown) on one end for connecting the connector segment 510 to theinternally threaded end (not shown) of a single-member drill string 512.The connector segment 510 may have an internal conduit (not shown)through which the pressurized fluid flows from the hydraulic hose 502 tothe gripper assembly 504. Thus, the other end of the connector segment510 forms a sealed connection with the gripper assembly 504.

Alternatively, the pressurized fluid for operating the device may besupplied through the drill pipe 14 (FIG. 1). If a dual-member drillstring having a solid inner pipe is used, the hydraulic fluid could flowthrough the annulus between the inner pipe and the hollow outer pipe. Ifthe inner pipe of the dual-member drill string is hollow, the fluidcould be supplied to the pipe-bursting apparatus through the innermember. If the boring operation employs the use of a single pipe drillstring, the hydraulic fluid may be supplied to the pipe-burstingapparatus 24D through an internal passage (not shown).

The gripper assembly 504 uses the pressurized fluid to apply pressure tothe inner surface 516 of the old pipe 500 to hold the pipe-burstingapparatus 24E in place while the hydraulic cylinder assembly 506 isoperated. Hydraulic pressure within the gripper assembly 504 increasesin response to resistance encountered by pulling the pipe-burstingmember 508 through the old pipe 500 in direction X. The gripper assembly504 may comprise a plurality of pistons 518 which provide the gripperassembly with sufficient frictional force to grip the inner surface 516of the old pipe 500 and hold the pipe-bursting apparatus 24E in a fixedposition during operation of the pipe-bursting member 508.

While the gripper assembly 504 holds the pipe-bursting apparatus 24E ina fixed position, the hydraulic cylinder assembly 506 operates on acylinder rod 520 to pull the pipe-bursting member 508 in direction X andthrough the old pipe 500. The cylinder rod 520 may be constructed fromany material that is resilient enough to withstand repetitive intenseaxial forces exerted upon the cylinder rod by the hydraulic cylinderassembly 506.

The cylinder rod 520 is connected to the pipe-bursting member 508 usinga threaded connection (not shown). The pipe-bursting member 508comprises a pipe-splitting bell 522. The pipe-splitting bell 522 has agenerally conical shape, one or more pipe-cutting blades 524 spacedabout the circumference of the member, and a connection member 526 toallow towing of the replacement pipe 528. The pipe-splitting bell 522has a conical shape to force fragments of the old pipe 500 into thesurrounding soil. Additionally, the pipe-splitting bell 522 may be sizedso that it will act to enlarge the existing borehole and facilitateinsertion of a new pipe 528 having a larger diameter than the old pipe500.

Pipe-bursting apparatus 24E operates like pipe-bursting apparatus 24D,the operation of which does not bear repeating here. However, thehydraulic pump used with the present embodiment may reside above-groundand does not require energy from the rotating inner member of thedual-member drill string.

It will now be appreciated that any one of the previously discussedpipe-bursting apparatuses may have several sensors to provide theoperator with operational information. For example, the pipe-burstingapparatus may have a plurality of sensors (not shown) supported by thehousing near the pipe-bursting member. The sensors may be adapted toprovide the operator with feedback regarding positioning ofpipe-bursting member, whether the pipe-bursting member is in theextended or retracted position, and the amount of force being exertedupon the old pipe by the pipe-bursting apparatus. Additionally, thepipe-bursting operation may be further assisted by a beacon (not shown)positioned near any one of the previously described pipe-burstingapparatuses. The beacon may be adapted to provide the operator withinformation about the position and orientation of the pipe-burstingapparatus.

The present invention also comprises a method for bursting pipe using ahorizontal directional drilling system 10. The method employs ahorizontal directional drilling machine and a dual-member drill string.A pipe-bursting apparatus is operatively connected to the second end ofthe dual-member drill string. Preferably one of the pipe-burstingapparatus, 24A, 24B, 24C, 24D, 25 or 27 as described herein, may be usedin carrying out this method.

Having determined the need for replacing the old pipe 16 without digginga trench, the dual-member drill string 14 is inserted through thesection of pipe to be replaced 16. The pipe-bursting apparatus isconnected to the downhole end of the drill string 14 as it protrudesfrom the far end of the old pipe. After connecting the pipe-burstingapparatus to the drill string 14, the apparatus is positioned within theold pipe by advancing, withdrawing or rotating the outer member. Oncethe pipe-bursting apparatus has been positioned, the inner member isrotated to operate the pipe-bursting apparatus. While the inner memberis rotated, the horizontal directional drilling machine may pull thedrill string, pipe-bursting apparatus, and replacement pipe through theold pipe.

Various modifications can be made in the design and operation of thepresent invention without departing from the spirit thereof. Thus, whilethe principal preferred construction and modes of operation of theinvention have been explained in what is now considered to represent itsbest embodiments, which have been illustrated and described, it shouldbe understood that within the scope of the appended claims, theinvention may be practiced otherwise than as specifically illustratedand described.

1. A pipe-bursting apparatus for use with a dual-member drill stringcomprising an outer member and an inner member, wherein the inner memberis rotatable independently of the outer member, the apparatuscomprising: a frame connectable with the drill string; a drive assemblysupported by the frame and operable in response to rotation of the innermember of the drill string; a rod rotatably supported within the frameand rotatable in response to operation of the drive assembly; and afirst pipe-bursting member supported by the frame and operativelyconnected to the rod; wherein the first pipe-bursting member is operablein response to rotation of the rod; a first movable wedge adapted toexpand the first pipe-bursting member, a second pipe-bursting membersupported by the frame and disposed in an opposing orientation to thefirst pipe-bursting member; a second movable wedge adapted to expand thesecond pipe-bursting member; and wherein the first and second wedges aresupported by the frame and operatively connected to the rod for movementtowards or away from each other in response to rotation of the rod. 2.The apparatus of claim 1 wherein the pipe-bursting member comprises atleast one blade operatively connected to the frame for movement inresponse to rotation of the rod.
 3. The apparatus of claim 1 wherein theframe comprises a housing having at least one opening, wherein the firstpipe-bursting member is retractable and expandable through the openingin response to rotation of the rod.
 4. The apparatus of claim 1comprising a screw drive supported by the frame for moving the firstpipe-bursting member between an expanded position and a retractedposition.
 5. The apparatus of claim 1 wherein the pipe-burstingapparatus further comprises: a movable collar operatively engaging therod for movement in response to rotation of the rod; and a movable armassembly attached to the movable collar and the frame, wherein themovable arm assembly actuates the pipe-bursting member between anexpanded position and a retracted position in response to movement ofthe collar.
 6. The apparatus of claim 5 wherein the movable collar andthe rod are threadedly engaged so that the collar travels along the rodas the rod rotates.
 7. The apparatus of claim 1 wherein thepipe-bursting member comprises an expansion bell.
 8. The apparatus ofclaim 7 wherein the expansion bell is adapted to threadingly engage atleast one of a plurality of screw drives supported on the rod andwherein the expansion bell is movable axially in response to rotation ofthe rod.
 9. The apparatus of claim 1 wherein the pipe-bursting membercomprises a pipe-engaging member pivotally connected to the frame formovement in response to rotation of the rod.
 10. The apparatus of claim1 wherein the frame comprises a housing having a first opening and asecond opening, wherein the first pipe-bursting member is retractableand expandable through the first opening in response to rotation of therod and wherein the second pipe-bursting member is retractable andexpandable through the second opening in response to rotation of therod.
 11. The apparatus of claim 1 wherein the frame comprises a housinghaving at least one opening, wherein the first pipe-bursting member isretractable and expandable through the opening in response to rotationof the rod.
 12. A pipe-bursting apparatus for use with a dual-memberdrill string comprising an outer member and an inner member, wherein theinner member is rotatable independently of the outer member, theapparatus comprising: a frame connectable with the drill string; a rodrotatably supported within the frame and connectable with the innermember of the drill string; a plurality of pipe-bursting membersoperatively connected to the frame; a plurality of screw drivessupported by the frame and operable in response to rotation of the rod,wherein operation of at least one of the plurality of screw drives driveoperation of the pipe-bursting members.
 13. The pipe-bursting apparatusof claim 12 wherein the pipe-bursting members comprise a plurality ofblades operatively connected to the frame and operable in response torotation of the inner member of the drill string.
 14. The pipe-burstingapparatus of claim 12 further comprising a gripper assembly supported bythe frame and operable in response to rotation of the rod.
 15. Thepipe-bursting apparatus of claim 12 further comprising: a movable collaroperatively engaging at least one of the plurality of screw drives formovement in response to rotation of the rod; and a movable arm assemblyattached to both the movable collar and the frame, wherein the movablearm assembly actuates the pipe-bursting member between an expandedposition and a retracted position in response to movement of the collar.16. The pipe-bursting apparatus of claim 15 wherein the movable armassembly comprises a four-bar linkage driven by the movable collar. 17.The pipe-bursting apparatus of claim 12 wherein the pipe-burstingapparatus further comprises at least one wedge adapted to engage thepipe-bursting member and adapted to drive operation of the pipe-burstingmember in response to rotation of the rod.
 18. The pipe-burstingapparatus of claim 12 wherein at least one of the pipe-bursting memberscomprises an expansion bell that operatively engages at least one of thescrew drives.
 19. The pipe-bursting apparatus of claim 18 wherein theexpansion bell is moved axially in response to operation of the at leastone screw drives.
 20. The pipe-bursting apparatus of claim 12 furthercomprising a drive assembly supported by the frame and connected to theinner member of the drill string, wherein the drive assembly is operablein response to rotation of the inner member of the drill string to driverotation of the rod.
 21. The pipe-bursting apparatus of claim 12 furthercomprising a first pipe-bursting member engaging wedge adapted to expandat least one of the pipe-bursting members and a second pipe-burstingmember engaging wedge adapted to expand at least another of thepipe-bursting members, wherein the first and second pipe-bursting memberengaging wedges are supported by the frame and operatively connected tothe rod for movement towards or away from each other in response torotation of the rod.
 22. The pipe-bursting apparatus of claim 12 whereinthe pipe-bursting members comprise a plurality of pipe-engaging membersconnected to the frame and operable in response to rotation of the innermember of the drill string.
 23. A horizontal directional drilling systemcomprising: a drive machine; a dual-member drill string, having a firstend and a second end; wherein the first end of the drill string isoperatively connected to the drive machine wherein the drill stringcomprises an inner member and an outer member, wherein the inner memberis moveable independently of the outer member; and a pipe-burstingapparatus operatively connected to the second end of the drill string sothat movement of the inner member drives operation of the apparatus, theapparatus comprising: a frame; a rod rotatably supported within theframe and rotatable in response to movement of the inner member of thedrill string; a plurality of pipe-bursting members operatively connectedto the frame; and a plurality of screw drives supported by the frame andoperable in response to rotation of the rod, wherein operation of atleast one of the plurality of screw drives drive operation of theplurality of pipe-bursting members.
 24. The horizontal directionaldrilling system of claim 23 wherein the pipe-bursting members comprise aplurality of blades operatively connected to the frame for movement inresponse to movement of the inner member of the drill string.
 25. Thehorizontal directional drilling system of claim 23 further comprising agripper assembly supported by the frame and operable in response tomovement of the inner member.
 26. The horizontal directional drillingsystem of claim 23 further comprising: a movable collar operativelyengaging at least one of the plurality of screw drives for movement inresponse to rotation of the rod; and a movable arm assembly attached toboth the movable collar and the frame, wherein the movable arm assemblyactuates the pipe-bursting members between an expanded position and aretracted position in response to movement of the collar.
 27. Thehorizontal directional drilling system of claim 26 wherein the movablearm assembly comprises a four-bar linkage driven by the movable collar.28. The horizontal directional drilling system of claim 23 wherein thepipe-bursting apparatus further comprises at least one pipe-burstingmember engaging wedge supported by the frame and operable in response torotation of the rod to drive operation of the pipe-bursting member. 29.The horizontal directional drilling, system of claim 23 wherein at leastone of the pipe-bursting members comprises an expansion bell supportedby the frame.
 30. The horizontal directional drilling system of claim 29wherein the expansion bell is moved axially in response to operation ofat least one of the screw drives.
 31. The horizontal directionaldrilling system of claim 23 further comprising a drive assemblysupported by the frame and connected to the inner member of the drillstring, wherein the drive assembly is operable in response to rotationof the inner member of the drill string to drive rotation of the rod.32. The horizontal directional drilling system of claim 23 furthercomprising a first wedge adapted to engage a first pipe-bursting memberto expand the first pipe-bursting member and a second wedge adapted toengage a second pipe-bursting member and to expand the secondpipe-bursting member, wherein the first and second wedges are supportedby the frame and operatively connected to the rod for movement towardsor away from each other in response to rotation of the rod.
 33. Thehorizontal directional drilling system of claim 23 wherein thepipe-bursting members comprise a plurality of pipe-engaging memberspivotally connected to the frame for movement in response to movement ofthe inner member of the drill string.